67. The answer is A. Predator Prey relationships have actually been found to be the most beneficial in ecosystems with high biodiversity. Predators and prey keep each other from becoming too over or underpopulated because when prey population is lacking, predators population decreases as well due to starvation. When predator population is high, prey population decreases and then the cycle continues, more predators die from starvation.
68. The answer is H. It's actually very interesting that cellular respiration and photosynthesis are almost opposite chemical equations. Photosynthesis takes in what cellular respiration removes. They even each other out.